In some types of automatic workpiece processing, workpieces are located and clamped in pallets and the pallets are progressively transferred from station to station of a multiple station transfer machine on slide rails or the like. In each station, these pallets are accurately located and clamped by a mechanism referred to as a pallet registry.
Pallet registries of a variety of types have been in use in industry for many decades. Several such registry mechanisms are shown in U.S. Pat. Nos. 2,672,675; 2,673,386; 3,155,217; 3,571,872; 3,968,869; 4,201,284; and my copending application, Ser. No. 164,092, filed June 30, 1980 now U.S. Pat. No. 4,362,233. Reference is also made to my copending application, Ser. No. 196,216 filed Oct. 14, 1980, now U.S. Pat. No. 4,360,097. These pallet registries and others can be categorized into two types: a first type, in which each registry is operated by one or more hydraulic cylinders, and a second type in which multiple registries are ganged together and operated by a single power source such as a cylinder or suitable mechanical device.
Registries of the first type, which are self-powered, employ locating pins and clamps which may be mechanically interlocked or operated by separate cylinders and are characterized by having relatively large movement capability of the clamping members for the pallet.
Registries of the second type, in which a group of registries is actuated by a single power means, are characterized by having the locating pins directly actuated by the common power means, while the clamp members are actuated by, or through, elastic members such as relatively low work output springs and the clamp member movement ranges are therefore relatively small. Accordingly, the amount of wear which can be tolerated on the clamp members and/or the associated clamp surface on the pallets is very small. Stated another way, a small amount of wear on either the clamp members or the associated clamp surface of the pallet will create a large change in the clamping force or even no clamping force at all. When the clamp surface of the pallet consists of one side of a horizontal plate member, known as a pallet foot, and the opposite side of the foot is the sliding surface on which the pallet slides from station to station, as is generally the case, then wear on this pallet foot slide surface and/or wear of the associated fixed rail further magnifies the problem of variable clamp force, or zero clamp force, due to wear. The aggregate wear on the slide rails, pallet foot, pallet clamp surface, and the clamp member greatly affects the clamp force because of the small amount of available clamp member movement. When the aggregate wear exceeds this clamp member movement, the clamp force drops to zero.
It is one object of this invention to provide a pallet registry design in which a group of registries may be ganged together and operated by a single power means while providing a clamp member movement of significantly greater range than those of present designs.
In present registry designs of the second type, in which multiple registries are operated by a single power means, the locating pins in each registry are directly actuated by that power means. Therefore, a slight mislocation of a pallet in any given registry will cause the entire power means to stall or break a component in the offending registry because all the force generated by the common power means is concentrated on the offending registry.
It is, therefore, another object of this invention to provide a pallet registry in which multiple registries are operated by a common power source, but the locating pins, as well as the clamp members, are independently actuated by individual internal elastic members when the common power source is operated.
In present registry designs, the clamp members are generally actuated by wedges, either straight line or circular, or screws, which are low efficiency mechanisms. Low efficiency refers to the fact that the work (force times distance) output from the mechanism is much less than the work into the mechanism, the loss being due to friction. Not only does the friction detract significantly from the theoretical force output of a wedge or screw mechanism, but variations in friction cause larger changes in the force output than such variations make in higher efficiency mechanisms.
It is a further object of this invention to provide a pallet registry in which the clamping force is transmitted from a power source to the clamp members through high efficiency mechanisms, such as simple levers, pivots, and rolling contacts.
In present registry designs, the reactive loads, due to the clamping forces, on the locating and structural components of the registry appear as significant bending loads thereon.
It is another object of this invention to provide a registry in which the bending loads due to clamping are primarily confined to members whose deflection does not affect the accuracy of pallet location, and in which the bending loads imposed on the locating and structural components of the registry are minimized to achieve lower deflections per unit of clamping force.
In many present registry designs, the transfer system operates above and through the pallet registry. Therefore, from a maintenance standpoint, in order to remove or replace a registry, it is necessary first to remove the transfer system, or parts of it, which increases the work and time required for maintenance.
It is, therefore, another object of this invention to provide a pallet registry which, by virtue of its inherent characteristics, can be made in two independent sub-assemblies which are mounted to the machine bed on each side of a substantially central transfer system, and one side or the other or both sides of the registry can be removed or replaced on the machine bed without removing the transfer system.
The movement of pallets through a transfer machine is presently accomplished in one of three ways: (1) they can be slid from station to station on fixed rails driven by a simple reciprocating transfer bar; or (2) they can be lifted and carried on transfer bars; or (3) they can be slide from station on rails which move through a small vertical stroke and utilize surfaces on the pallet which are different from the vertical locating surfaces. The first method, using fixed slide rails, suffers from the disadvantage of locating the pallets vertically on surfaces subject to wear, while the latter two methods have required more complex and expensive mechanisms.
It is another object of this invention to provide a simplified lift and carry type pallet transfer system or a vertically moving slide rail system, in which the vertical motion for either system, is generated by a simple addition to the registry actuation system.
Other objects of the invention will be apparent in the following description and claims in which, with the accompanying drawings, there is disclosed the principles of operation of the invention, together with details to enable a person skilled in the art to practice the invention all in connection with the best mode presently contemplated for the practice thereof.